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This paper deposited a layer of nanometer-sized Pt50-Sn50 catalyst particles in the proton exchange membrane (PEM) surface by impregnation-reduction (IR) method to suppress the methanol crossover and improve the utilization efficiency of methanol fuel. The suppression of methanol crossover and the performance of membrane electrode assembly (MEA) for the proposed structure were compared to those with normal-PEM structure. The possible mechanism of the suppression of methanol crossover was investigated. SEM, X-ray, EDS and EPMA analysis were used to characterize microstructures, phases, chemical composition and distributions for the obtained electro-catalyst layers. Methanol crossover rate in a DMFC was determined by measuring the CO2 concentration at the cathode exit in real time. Experimental results demonstrate that the PEM with a layer of nanometer-sized Pt50-Sn50 catalyst particles suppresses methanol crossover by up to 18% more than the normal-PEM, and yield a 8% better MEA performance than the normal-MEA. The combination effects of Pt50-Sn50 in PEM as a methanol filter and electrode contribute to the suppression of methanol crossover and improvement of cell performance as well as the utilization efficiency of methanol fuel.